Alumina agglomerates and process for the preparation thereof

ABSTRACT

Provided is a process for preparing alumina agglomerates which comprises: 
     (i) treating agglomerates of active alumina with an aqueous medium comprising at least one acid making it possible to dissolve at least part of the alumina and at least one compound providing an anion capable of combining with aluminum ions in solution, 
     (ii) subjecting the agglomerates to a hydrothermal treatment at a temperature in the range of from about 80° C. to about 250° C., and then 
     (iii) thermally activating the agglomerates at a temperature in the range of about 500° C. to about 1100° C. 
     The resulting alumina agglomerates possess exceptional mechanical strength, heat resistance and hydrothermal resistance and are useful as catalysts or catalyst supports.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 08/082,107,filed Jun. 28, 1993, which is a Divisional of application Ser. No.07/863,140, filed Apr. 2, 1992, now U.S. Pat. No. 5,244,648, which is acontinuation of application Ser. No. 07/737,902, filed Jul. 26, 1991,abandoned: which is a continuation of application Ser. No. 07/169,121,filed Mar. 9, 1988, abandoned; which is a continuation of applicationSer. No. 06/876,826, filed Jun. 20, 1986, abandoned; which is acontinuation of application Ser. No. 06/508,575, filed Jun. 28, 1983,abandoned; which is a continuation-in-part of application Ser. No.06/330,000, filed Dec. 11, 1981, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for the preparation ofalumina agglomerates of controlled porosity, which agglomerates possessexceptional mechanical strength, heat resistance and hydrothermalresistance.

2. Description of the Prior Art

A process for the regeneration of a composite catalyst containingalumina by heating the spent catalyst in a medium containing a majorproportion of acetic acid and a minor proportion of hydrochloric acid isdisclosed in U.S. Pat. No. 2,651,617. The heat treatment is at atemperature of from 200 to 250° C. The process reduces the density ofthe spent catalyst by removing part of the alumina contained in thecomposite treated to thereby provide a porous particle. The acids areused in concentrated form, i.e., at least 60% strength by weight.

French Patent No. 1,222,830 discloses a process for the manufacture ofalumina supports for catalysts which comprises treating the alumina at atemperature below 80° C. in a concentrated acid medium to therebydissolve a portion of it. The dissolved portion is then removed in theform of aluminum chloride by washing with water.

French Patent No. 1,386,364, of common assignee, discloses a process forpreparing alumina agglomerates possessing a high mechanical strength. Inthe process disclosed, agglomerates of active alumina are treated in anautoclave in the presence of water, dried and then calcined at atemperature providing the specific surface area and desired pore size.

According to U.S. Pat. Nos. 3,628,914 and 3,480,389, also of commonassignee, alumina agglomerates are prepared of even higher mechanicalstrength than that obtained according to French Patent No. 1,386,364 bytreating agglomerates of active alumina with an acid in an autoclave.

It is an object of the present invention, however, to provide aluminaagglomerates of exceptional mechanical strength, heat resistance andhydrothermal resistance.

It is another object of the present invention to provide a process whichmakes it possible to obtain alumina agglomerates possessing a controlledporosity together with exceptional mechanical strength, i.e., attritionresistance and crushing strength.

It is still another object of the present invention to provide a processfor preparing alumina agglomerates possessing not only a controlledporosity and excellent mechanical strength at high temperatures, buteven in the presence of steam so that the alumina agglomerates exhibitvaluable heat stability and hydrothermal stability.

It is further an object of the present invention to provide a processfor preparing alumina agglomerates possessing all of the aforementioneddesirable characteristics, and which does not result in any loss ofalumina, in contrast to those processes described in U.S. Pat. No.2,651,617 and French Patent No. 1,222,830.

These and other objects, as well as the scope, nature and utilization ofthe invention, will be apparent to those skilled in the art from thefollowing description and the appended claims.

SUMMARY OF THE INVENTION

A process which achieves all of the aforegoing objectives has now beensuccessfully developed. The alumina agglomerates obtained thereby can beused as catalysts or catalyst supports in any reaction which requires aparticular pore structure together with very good mechanical, thermaland hydrothermal properties. Alumina agglomerates prepared by theprocess of the present invention find particular applicability in thetreatment of the exhaust gases of internal combustion engines, inhydrodesulfurization, hydrodemetallation, and hydrodenitrificationreactions, and, in general, in any hydrogen treatment of petroleumproducts.

The process of the present invention, which provides aluminaagglomerates of controlled porosity, exceptional mechanical strength,heat resistance and hydrothermal resistance, is characterised in that:

(i) active alumina agglomerates are treated with an aqueous mediumcomprising at least one acid making it possible to dissolve at leastpart of the alumina of the agglomerates, and of at least one compoundproviding an anion capable of combining with the resulting aluminum ionsin solution,

(ii) subjecting the agglomerates, either simultaneously or subsequentlyto the aqueous medium treatment, to a hydrothermal treatment at atemperature between about 80° C. and about 250° C., preferably for aperiod of time ranging from about a few minutes to about 36 hours, andthen

(iii) drying the agglomerates, if appropriate, and subjecting same tothermal activation at a temperature in the range of from about 500° C.to about 1,100° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a scanning electron microscope image (magnification of10,000X) of the surface of a fragment of an alumina agglomerate of thepresent invention obtained according to Example 1.

FIG. 2 depicts a scanning electron microscope image (magnification of3000X) of a group of alumina agglomerates prepared according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The agglomerates of active alumina used in the process of the presentinvention are prepared from a powder of active alumina having a poorlycrystalline and/or amorphous structure, which can be obtained, forexample, in accordance with a process such as that described in FrenchPatent No. 1,438,497. Such a process consists of moistening activealumina having a poorly crystalline and/or amorphous structure by usingan aqueous solution, agglomerating it, and aging the resultingagglomerates in a moist atmosphere at a relatively low temperature,preferably at a temperature between about 60 and 100° C. Theagglomerates are dried and then calcined at a temperature between about250° C. and about 900° C.

The expression "alumina of poorly crystalline structure" for thepurposes of the aforegoing process is understood as meaning an aluminawhich is such that X-ray analysis gives a pattern which shows only oneor a few diffuse lines corresponding to the crystalline phases of thelow-temperature transition aluminas, and contains essentially the chi,rho, eta, gamma and pseudo-gamma phases and mixtures thereof.

By the expression "alumina of amorphous structure" is meant an aluminawhich is such that its X-ray analysis does not give any linecharacteristic of a crystalline phase.

The active alumina employed can be generally obtained by the rapiddehydration of aluminum hydroxides such as bayerite, hydrargillite orgibbsite, and nordstrandite, or of aluminum oxyhydroxides such asboehmite and diaspore. The dehydration can be carried out in anyappropriate apparatus, and by using a hot gaseous stream. Thetemperature at which the gases enter the apparatus can generally varyfrom about 400 to 1,200° C. and the contact time of the hydroxide oroxyhydroxide with the hot gases is generally between a fraction of asecond and 4 to 5 seconds.

The specific surface area of the active alumina obtained by the rapiddehydration of hydroxides or oxyhydroxides, as measured by theconventional BET method, generally varies between about 50 and 400 m²/g, and the diameter of the particles is generally between 0.1 and 300microns and preferably between 1 and 120 microns. The loss on ignition,measured by calcination at 1,000°, generally varies between 3 and 15%,which corresponds to a molar ratio H₂ O/Al₂ O₃ of between about 0.17 and0.85.

In a preferred embodiment, an active alumina originating from the rapiddehydration of Bayer hydrate (hydrargillite), which is a readilyavailable and inexpensive industrial aluminum hydroxide is employed.Active alumina of this type is well known to those skilled in the artand the process for its preparation has been described, for example, inFrench Patent No. 1,108,011.

The active alumina employed can be used as such or may be treated sothat its sodium hydroxide content, expressed as Na₂ O, is less than1,000 ppm. The active alumina employed may or may not be ground.

The agglomeration of the active alumina is carried out in accordancewith the methods well known to the art, and, in particular, by suchmethods as pelletizing, extrusion, shaping into beads in a rotatingcoating drum, and the like.

As is known to those skilled in the art, the agglomeration may becarried out with the addition of pore-forming agents to the mixture tobe agglomerated. The pore-forming agents which can be used inparticular, are wood flour, wood charcoal, cellulose, starches,naphthalene and, in general, all organic compounds capable of beingremoved by calcination.

If necessary, the aging, drying and/or calcination of the agglomeratesare then carried out.

The agglomerates of active alumina used in accordance with the processof the present invention generally have the following characteristics: aloss on ignition, measured by calcination at 1,000° C., between about 1and about 15%; a specific surface area between about 100 and about 350m² /g; and, a total pore volume between about 0.45 and about 1.2 cm³ /g.

The agglomerates of active alumina are treated in accordance with theprocess of the present invention, with an aqueous medium comprising amixture of at least one acid making it possible to dissolve at leastpart of the alumina of the agglomerates, and of at least one compoundproviding an anion capable of combining with aluminum ions in solution.

By the expression "acid making it possible to dissolve at least part ofthe alumina of the agglomerates", as utilized herein, is meant any acidwhich, when brought into contact with the agglomerates of active aluminaas defined above, brings at least some of the aluminum ions intosolution. Generally, the acid must dissolve from 0.5% to about 15% byweight of alumina of the agglomerates. Its concentration in the aqueoustreatment medium is generally less than 20% by weight and preferablybetween 1% and 15%.

It is preferred to use strong acids such as nitric acid, hydrochloricacid, perchloric acid and sulfuric acid. Weak acids used at aconcentration such that their aqueous solution has a pH of less thanabout 4 can also be used.

By the expression "compound providing an anion capable of combining withthe aluminum ions in solution", as utilized herein, is intended anycompound which is able to release, in solution, an anion A^(-n) capableof forming products with aluminum cations in which the atomic ratio##EQU1## A particular illustration of such products are the basic saltsof the general formula Al₂ (OH)_(x) A_(y), in which 0<x<6, ny<6 and nrepresents the number of charges on the anion A.

The concentration of this anion donor compound in the aqueous treatmentmedium is less than 50% by weight and preferably between 3% and 30%.

It is preferred to use compounds which release, in solution, nitrite,chloride, sulfate, perchlorate, chloroacetate, dichloroacetate,trichloroacetate, bromoacetate and dibromoacetate anions, as well asanions of the general formula ##STR1## in which R represents a radicalselected from the group consisting of H, CH₃, C₂ H₅, CH₃ CH₂ CH₂ and(CH₃)₂ CH.

The compounds which are capable of releasing the anion A^(-n) insolution can effect this release either directly, for example bydissociation, or indirectly, for example by hydrolysis. Illustrativecompounds include, in particular, mineral or organic acids, anhydrides,organic or inorganic salts, and esters. Among the inorganic salts, theremay be mentioned water soluble alkali metal or alkaline earth metalsalts, such as salts of sodium, potassium, magnesium or calcium,ammonium salts, aluminum salts and rare earth salts.

This first treatment can be carried out either by dry impregnation ofthe agglomerates, or by immersion of the agglomerates in an aqueoussolution of the mixture of acid and anion donor compound. By theexpression "dry impregnation" as used herein is meant the contacting ofthe alumina agglomerates with a volume of solution which is less than orequal to the total pore volume of the agglomerates treated.

In a preferred embodiment of the present invention, mixtures of nitricacid and acetic acid or of nitric acid and formic acid are used as theaqueous medium.

The aforedescribed treated agglomerates are simultaneously orsubsequently subjected to a treatment at a temperature between about 80and about 250° C., for a period of time of between about a few minutesand about 36 hours.

This hydrothermal treatment does not result in any loss of alumina.

The treatment is preferably carried out at a temperature between 120 and220° C., for a period of time of between 15 minutes and 18 hours.

The treatment constitutes a hydrothermal treatment of the agglomeratesof active alumina, which effects the conversion of at least some of theagglomerates to boehmite. The hydrothermal treatment can be carried outeither under saturated steam pressure or under a partial steam pressureequal to at least 70% of the saturated steam pressure which correspondsto the treatment temperature.

Without being limited to theory, it is believed that the association ofthe acid, which is capable of dissolving at least part of the aluminawith the aforediscussed anion during the hydrothermal treatment resultsin the production of a particular boehmite which imparts, to thecalcined agglomerates, their excellent heat resistance and hydrothermalresistance.

Furthermore, since the concentration of the acid and anion donorcompound in the treatment mixture and the conditions of the hydrothermaltreatment used are such that there is no loss of alumina, the increasein the porosity following the treatment is therefore due to an expansionof the agglomerates during the treatment and not to a loss of alumina.

The agglomerates thus treated are then dried, if deemed appropriate, ata temperature which is generally between 100 and 200° C., for asufficient period of time to remove the water which is not chemicallybound. The agglomerates are then subjected to a thermal activationtreatment at a temperature in the range of from about 500° C. to about1,100° C. for a period of time generally between about 15 minutes and 2hours.

The activation treatment can be carried out in several steps, with theactivation most preferably being carried out at a temperature in therange of from about 550 to about 950° C. Depending on the particularactivation temperature employed, the alumina agglomerates predominantlyexhibit the crystal structure characteristic of their boehmitefiliation.

The alumina agglomerates prepared according to the present invention arecharacterized by the juxtaposition of a plurality of elementary units,designated agglomerates, each agglomerate being comprised by a pluralityof acicular platelets, generally oriented with respect to each other asthe radii of a sphere, the center of which coincides with that of theagglomerate. As a general rule, at least 50% of the acicular platelets,have a dimension along their axis of greatest development between about0.05 and 5 microns and preferably between about 0.1 and 2 microns, aratio of this dimension to their average width of between about 2 and 20and preferably between about 5 and 15, a ratio of this dimension totheir average thickness of between about 1 and 500 and preferablybetween about 10 and 200. A large proportion, for example at least about50% of the agglomerates of acicular platelets, comprise a collection ofsubstantially or pseudo-spherical particles of an average size of about1 to 20 microns, preferably between about 2 and 10 microns. A highlyadequate image to represent such a structure is, for example, a pile ofprickly chestnut burs, or a pile of sea-urchins.

The technique of scanning electron microscopy makes it possible tocharacterize without ambiguity by means of micrographs an aluminaagglomerate of the present invention. FIGS. 1 and 2 depict aluminaagglomerates according to the present invention, which illustrate wellthe particular structure of juxtaposed urchins described hereinabove.

The active alumina agglomerates prepared by the process of the presentinvention generally possess the following physical properties:

A tapped density (TD) of between about 0.36 and about 0.75 g/cm³. ThisTD is measured in the following manner: A given weight of agglomeratesis introduced into a graduated cylinder. The cylinder is then caused tovibrate until all settling has ceased and until a constant volume isobtained. The weight of agglomerates per unit volume is then calculated.

A total pore volume (TPV) of from about 0.35 to about 1.50 cm³ /g. TheTPV is determined from the particle density and the absolute density,with the particle density (Dp) and absolute density (Da) being measuredby the pycnometry method respectively using mercury and helium. The TPVis given by the formula ##EQU2##

A distribution of pore volumes according to the size of the pores (DIS),such that:

    ______________________________________                                        φ in Å                                                                      <100    100-1,000                                                                              1,000-5,000                                                                           5,000-10,000                                                                           >10,000                               ______________________________________                                        ν cm.sup.3 /g                                                                    0-0.10  0.40-0.90                                                                              0-0.60  0-0.55   0.040                                 ______________________________________                                    

in which Φ represent the diameter of the pores and ν the volume of thepores having a diameter between the limits indicated.

The DIS in the agglomerates is determined by the mercury penetrationtechnique, in which Kelvin's law is applied, and which gives therelationship between the pressure, the diameter of the smallest poreinto which the mercury penetrates at the said pressure, the contactangle and the surface tension, according to the formula: ##EQU3## inwhich Φ represents the diameter of the pore, t the surface tension, othe contact angle and p the pressure.

A specific surface area (SSA), as measured by the B.E.T. method, of fromabout 80 to about 200 m² /g.

A mechanical strength (PPC) of from about 2 to about 29 kg. Themechanical strength is measured by the particle-by-particle crushingmethod (PPC). It consists in measuring the maximum compression forcewhich a granule can withstand before it breaks by placing the productbetween two planes moving at a constant speed of 5 cm/minute. In theparticular case of spheres, the force is expressed in kilograms. In thecase of extrudates or pellets, the compression is appliedperpendicularly to one of the generatrices of the product, and theparticle-by-particle crushing is expressed as the ratio of the force tothe length of the generatrix and will thus be in kilograms/mm.

The mechanical strength (PPC) is related to the total pore volume (TPV)by Schiller's law: ##EQU4## in which A and B are constants, Thus, whenthe porosity of a product (TPV) increases, the PPC decreases, and it istherefore difficult to manufacture products which are both porous andstrong.

An attrition resistance (AR) of more than about 98%. The attritionresistance is measured as the percentage of product which is not wornaway by friction in accordance with the following method: a given volume(60 cm³) of agglomerate is introduced into an upturned Erlenmeyer flaskof particular construction, which is connected to a metal inlet orifice.A large outlet orifice (2.54 cm) covered with a sieve of mesh size 1.168mm is positioned in the bottom of the Erlenmeyer flask. A strong streamof dry nitrogen is passed through the inlet orifice. The nitrogen streamhas two purposes, first, to cause the agglomerates to circulate andcollide with one another, which results in their wear by friction, andsecond to cause the agglomerates to impact against the Erlenmeyer flask,which results in their degradation proportional to the intensity of theimpact. The product is tested for 5 minutes and the weight ofagglomerates remaining is measured. The decrease in weight after theexperiment, expressed as a percentage of the initial charge, representsthe attrition resistance AR.

A shrinkage (Sh) of less than 2% after heat treatment for 24 hours indry air at 982° C. or 1093° C. The shrinkage is measured as thepercentage decrease in volume of the agglomerates, which is determinedin the following manner: A given amount of agglomerates is introducedinto a graduated cylinder and the latter is vibrated until all settlinghas ceased and until a constant volume is obtained, as in measuring theTD. The agglomerates are then heat treated under dry air for 24 hours,either at 982° C. or at 1,093° C. The volume of the agglomerates aftervibration is then again measured and the decrease in volume after theheat treatment is calculated, relative to the initial volume, andexpressed as a percentage of the decrease in volume.

Furthermore, the agglomerates of the instant invention as prepared bythe process thereof possess excellent properties after heat treatment orhydrothermal treatment.

After heat treatment at 982° C. (HT 982° C.) for 24 hours under dry air,their characteristics are generally as follows:

SSA>60 m² /g

PPC between 2 and 20 kg

AR>98%

Sh<2%

After heat treatment at 1,093° C. (HT 1,093° C.) for 24 hours under dryair, agglomerates of the present invention which have been stabilizedpreviously in accordance with the process disclosed in U.S. Pat. No.4,061,594, of common assignee, generally possess the followingcharacteristics:

SSA>50 m² /g

PPC between 2 and 20 kg

AR>98%

After a hydrothermal treatment at 900° C. (HT H₂ O, 900° C.) for 24hours under a nitrogen atmosphere containing 10% steam, agglomerates ofthe present invention generally possess the following characteristics:

SSA>60 m² /g

PPC between 2 and 20 kg

AR>98%

From the aforegoing properties, it is clearly evident that the processof the present invention provides agglomerates of active alumina whichpossess excellent mechanical, thermal and hydrothermal properties and apore distribution which is readily adjusted within an extended range.

Moreover, the process of the present invention makes it possible, inparticular and totally unexpectedly, to modify the pore volumedistribution of the different pore sizes of the untreated agglomerates.For example, the proportion of pores between 100 and 1,000 Å, can beincreased, and the proportion of pores less than 100 Å and greater than5,000 and/or 10,000 Å can be reduced while only slightly modifying theproportion of pores between 1,000 and 5,000 Å. The process according tothe present invention thus makes it possible to obtain, as is desired,microporous and/or macroporous products possessing exceptionalproperties.

The alumina agglomerates obtained via the process of the presentinvention can be employed as catalysts or catalyst supports. If sorequired, the alumina agglomerates can be heat-stabilized with rareearths, silica or alkaline earth metals as is well known to thoseskilled in the art. In particular, they can be stabilized in accordancewith the process described in U.S. Pat. No. 4,061,594, of commonassignee.

The alumina agglomerates of the present invention can be used, inparticular, as catalyst supports in processes involving very rapidreactions with very limited internal diffusion, and in reactions lendingto progressive poisoning of the catalyst. In such cases, theagglomerates of the present invention having a bimodal pore structure(containing micropores and macropores) are particularly effective, asthe impurities are trapped in the macropores while the micropores remaincatalytically active. Prepared agglomerates which are particularlysuitable for such a purpose have, in particular, a pore distributionsuch that: the volume of pores with a diameter greater than 10,000 Å isgreater than 0.10 cm³ /g, the volume of pores with a diameter between1,000 Å and 10,000 Å is between 0.10 and 0.15 cm³ /g, the volume ofpores with a diameter of between 100 and 1,000 Å is between 0.50 and0.80 cm³ /g and the volume of pores with a diameter less than 100 Å isless than 0.05 cm³ /g.

The active alumina agglomerates of the present invention can thus findparticular applicability as catalyst supports in the treatment ofexhaust gases generated by internal combustion engines and in hydrogentreatments of petroleum products, such as hydrodesulfurization,hydrodemetallation and hydrodenitrification. They can also be used ascatalyst supports in reactions for the recovery of sulfur from sulfurcompounds (Claus catalysis), the dehydration, reforming, steamreforming, dehydrohalogenation, hydrocracking, hydrogenation,dehydrogenation, and dehydrocyclization of hydrocarbons or other organiccompounds, as well as oxidation and reduction reactions.

If the agglomerates obtained in accordance with the process of thepresent invention are used as catalyst supports for treating the exhaustgases from internal combustion engines, the active phase thereof canadvantageously be the one described in French Patent No. 79/24,675, ofcommon assignee.

The following examples are given as specific illustrations of theclaimed invention. It should be understood, however, that the specificdetails set forth in the examples are merely illustrative and in nowiselimitative. All parts and percentages in the examples and the remainderof the specification are by weight unless otherwise specified.

EXAMPLE 1

4 kg of alumina beads obtained in accordance with the process describedin French Patent No. 1,438,497 were treated in a 10 liter reactor. Thealumina beads possessed the following characteristics:

PPC: 1.0 kg

SSA: 192 m² /g

TPV: 0.84 cm³ /g

DIS:

    ______________________________________                                        φ Å                                                                         <100    100-1,000                                                                              1,000-5,000                                                                           5,000-10,000                                                                           >10,000                               ______________________________________                                        ν cm.sup.3 /g                                                                    0.06    0.04     0.05    0.05     0.28                                  ______________________________________                                    

The treatment was carried out in the vapor phase at a temperature of195° C. for a period of 3 hours. The treatment medium consisted of amixture of nitric acid and acetic acid. The concentration of nitric acidwas 7 g per 100 g of Al₂ O₃, and the concentration of acetic acid was 10g per 100 g of Al₂ O₃. The nitric acid made it possible to dissolveabout 2.5% by weight of the alumina beads. The acetic acid providedacetate anion, which combined with the aluminum ions in solution to formcompounds in which the atomic ratio ##EQU5## was less than 3.

The beads thus treated were thermally activated in a furnace at 900° C.for 1 hour and are depicted in FIG. 1.

The properties of the beads obtained were determined in accordance withthe methods which have been described above. The beads possessed thefollowing characteristics:

TD: 0.44 g/cm³

TPV: 1.05 cm³ /g

DIS:

    ______________________________________                                        φ Å                                                                         <100    100-1,000                                                                              1,000-5,000                                                                           5,000-10,000                                                                           >10,000                               ______________________________________                                        ν cm.sup.3 /g                                                                    0.01    0.68     0.10    0.07     0.19                                  ______________________________________                                        SSA:       107 m.sup.2 /g                                                     PPC:       3.6 kg                                                             AR:        99.7%                                                              HT 982° C.:                                                            SSA:       75 m.sup.2 /g                                                      PPC:       3.3 kg                                                             AR:        99.6%                                                              Sh:        0.8%                                                               HT 1,093° C.:                                                          SSA:       71 m.sup.2 /g                                                      PPC:       3.8 kg                                                             AR:        99.7%                                                              HT H.sub.2 O, 900° C.:                                                 SSA:       84 m.sup.2 /g                                                      PPC:       3.4 kg                                                             AR:        99.4%                                                              ______________________________________                                    

As can be seen from the aforegoing, these beads possess exceptionalmechanical, thermal and hydrothermal properties. The treatment carriedout made it possible, totally unexpectedly, to simultaneously increasethe strength and pore volume of the beads. This apparent contradictionto Schiller's law is explained by a modification of the constants A andB due to the treatment effected. The treatment made is possible tovirtually eliminate pores with a diameter less than 100 Å, to increasethe number of pores with a diameter of between 100 and 1,000 Å and toslightly reduce the number of pores with a diameter greater than 10,000Å.

EXAMPLE 2

4 kg of alumina beads prepared in accordance with the process describedin French Patent No. 1,438,497 were treated in a 10 liter reactor. Thebeads possessed the following characteristics:

SSA: 135 m² /g

TPV: 0.82 cm³ /g

DIS:

    ______________________________________                                        φ Å                                                                         <100    100-1,000                                                                              1,000-5,000                                                                           5,000-10,000                                                                           >10,000                               ______________________________________                                        ν cm.sup.3 /g                                                                    0.06    0.48     0.04    0.03     0.21                                  ______________________________________                                    

The treatment was carried out in the vapor phase at a temperature of151° C. for a period of 15 hours. The treatment medium consisted of amixture of nitric acid and formic acid, with the concentration of nitricacid being 7 g/100 g of Al₂ O₃, and the concentration of formic acidbeing 6 g/100 g of Al₂ O₃. The nitric acid resulted in a dissolution ofabout 2.5% of the alumina beads. The formic acid provided the formateanion, which combined with the aluminum ions in solution to formcompounds in which the atomic ratio ##EQU6## was less than 2.5.

The beads thus treated were thermally activated in a furnace at 900° C.for 1 hour.

The properties of the beads prepared were tested in accordance with themethods which have been described above. The beads possessed thefollowing characteristics:

TD: 0.49 g/cm³

TPB: 0.91 cm³ /g

DIS:

    ______________________________________                                        φ Å                                                                         <100    100-1,000                                                                              1,000-5,000                                                                           5,000-10,000                                                                           >10,000                               ______________________________________                                        ν cm.sup.3 /g                                                                    0.02    0.57     0.04    0.11     0.17                                  ______________________________________                                        SSA:       115 m.sup.2 /g                                                     PPC:       4.7 kg                                                             AR:        99.4%                                                              HT 982° C.:                                                            SSA:       68 m.sup.2 /g                                                      PPC:       4.2 kg                                                             AR:        99.6%                                                              Sh:        1.1%                                                               HT 1,093° C.:                                                          SSA:       65 m.sup.2 /g                                                      PPC:       4.4 kg                                                             AR:        99.3%                                                              HT H.sub.2 O, 900° C.:                                                 SSA:       69 m.sup.2 /g                                                      PPC:       4.5 kg                                                             AR:        99.3%                                                              ______________________________________                                    

EXAMPLE 3

The experiment of Example 1 was repeated, modified only in thecharacteristics of the starting beads, which were as follows:

SSA: 257 m² /g

TPV: 0.54 cm³

DIS: <100=0.49 cm^(3/) g, 100-1,000=0.05 cm³ /g

The beads obtained after treatment as described in Example 1 possessedthe following characteristics:

TD: 0.53 g/cm³

TPV: 0.82 cm³ /g

DIS:

    ______________________________________                                        φ Å                                                                         <100    100-1,000                                                                              1,000-5,000                                                                           5,000-10,000                                                                           >10,000                               ______________________________________                                        ν cm.sup.3 /g                                                                    0.02    0.66     0.10    0.04     0                                     ______________________________________                                        SSA:       103 m.sup.2 /g                                                     PPC:       14 kg                                                              AR:        99.8%                                                              HT 982° C.:                                                            SSA:       69 m.sup.2 /g                                                      PPC:       13.2 kg                                                            AR:        99.6%                                                              Sh:        0.9%                                                               HT 1,093° C.:                                                          SSA:       66 m.sup.2 /g                                                      PPC:       13.7 kg                                                            AR:        99.4%                                                              HT H.sub.2 O, 900° C.:                                                 SSA:       75 m.sup.2 /g                                                      PPC:       12.5 kg                                                            AR:        99.3%                                                              ______________________________________                                    

As can be gained from the aforegoing properties, the beads possessedexceptional mechanical, thermal and hydrothermal properties. Treatmentin accordance with the process of the present invention increasedconsiderably the total pore volume, and in particular the pore volume ofpores having a diameter between 100 and 1,000 Å. The treatment alsoresulted in a production of pores having a diameter between 1,000 and10,000 Å.

EXAMPLE 4

The experiment of Example 1 was again repeated, this time modifying onlythe treatment conditions (temperature and time) of the beads in theaqueous medium. The physical characteristics and properties of the beadsprepared and the treatment conditions are given in Table I below.

                  TABLE I                                                         ______________________________________                                                   Time in hours                                                                 2     3       4       6     0.5                                    TREATMENT    T in ° C.                                                 CONDITIONS   195     195     195   195   215                                  ______________________________________                                        CHARACTERISTICS OF THE BEADS OBTAINED                                         TD (g/cm.sup.3)                                                                            0.48    0.44    0.43  0.39  0.44                                 TPV (cm.sup.3 /g)                                                                          0.93    1.05    1.09  1.24  1.04                                 DIS                                                                           <100 Å   0.01    0.01    0.00  0     0.01                                 100-1,000 Å                                                                            0.61    0.68    0.72  0.86  0.70                                 1,000-5,000 Å                                                                          0.07    0.10    0.12  0.10  0.08                                 5,000-10,000 Å                                                                         0.05    0.07    0.08  0.09  0.07                                 >10,000 Å                                                                              0.19    0.19    0.17  0.19  0.18                                 SSA (m.sup.2 /g)                                                                           108     107     106   103   105                                  PPC (kg)     4.0     3.6     3.6   3.2   3.8                                  AR (%)       99.5    99.7    99.7  99.6  99.6                                 HT 982° C.                                                             SSA (m.sup.2 /g)                                                                           71      75      73    69    74                                   PPC (kg)     3.8     3.3     3.4   3.0   3.5                                  AR (%)       99.4    99.6    99.6  99.3  99.4                                 Sh (%)       1.2     0.8     0.7   0.5   0.7                                  HT 1093° C.                                                            SSA (m.sup.2 /g)                                                                           67      71      69    65    69                                   PPC (kg)     3.8     3.8     3.4   3.1   3.7                                  AR (%)       99.3    99.7    99.6  99.2  99.6                                 HT H.sub.2 O, 900° C.                                                  SSA (m.sup.2 /g)                                                                           69      84      88    89    86                                   PPC (kg)     3.9     3.4     3.5   3.1   3.5                                  AR (%)       99.3    99.4    99.5  99.5  99.4                                 ______________________________________                                    

Thus, it can be seen that in the practice of the process of the presentinvention it is possible to adjust as desired, by modifying thetreatment time of the beads, the total pore volume and the pore volumeof pores having a diameter between 100 and 1,000 Å without significantlyeffecting the exceptional mechanical, thermal and hydrothermalproperties of the beads prepared.

EXAMPLE 5

The experiment of Example 1 was repeated, modified only with regard tothe treatment medium of the alumina beads. The physical characteristicsand properties of the beads prepared and the treatment medium employedare given in Table II below.

                  TABLE II                                                        ______________________________________                                        Treatment medium                                                              Acid (H.sup.+)                                                                Concentration by weight                                                                     CH.sub.3 COOH                                                                           HCl       HNO.sub.3                                   per 100 g of Al.sub.2 O.sub.3                                                               15%       4%        7%                                          Compound (A.sup.-)                                                            Concentration by weight                                                                     (NH.sub.4).sub.2 SO.sub.4                                                               (CH.sub.3 CO).sub.2 O                                                                   CH.sub.3 COOCH.sub.3                        per 100 g of Al.sub.2 O.sub.3                                                               12%       5%        6%                                          ______________________________________                                        Characteristics of the beads obtained                                         TD (g/cm.sup.3)                                                                             0.47      0.45      0.45                                        TPV (cm.sup.3 /g)                                                                           0.97      1.02      1.03                                        DIS                                                                           <100 Å    0.01      0.01      0.01                                        100-1,000 Å                                                                             0.62      0.66      0.67                                        1,000-5,000 Å                                                                           0.07      0.08      0.08                                        5,000-10,000 Å                                                                          0.06      0.08      0.08                                        >10,000 Å 0.21      0.19      0.19                                        SSA (m.sup.2 /g)                                                                            109       11        113                                         PPC (kg)      4.1       3.9       3.9                                         AR (%)        99.8      99.6      99.7                                        HT 982° C.                                                             SSA (m.sup.2 /g)                                                                            81        76        78                                          PPC (kg)      4.0       3.8       3.5                                         AR (%)        99.6      99.4      99.7                                        Sh (%)        0.4       0.8       0.7                                         HT 1,093° C.                                                           SSA (m.sup.2 /g)                                                                            71        71        72                                          PPC (kg)      3.8       3.6       3.6                                         AR (%)        99.3      99.4      99.6                                        HT H.sub.2 O, 900° C.                                                  SSA (m.sup.2 /g)                                                                            88        84        83                                          PPC (kg)      3.8       3.7       3.5                                         AR (%)        99.5      99.5      99.4                                        ______________________________________                                    

EXAMPLE 6

The experiment of Example 1 was repeated, modified only in the thermalactivation conditions (temperature, time) of the beads.

The physical characteristics and properties of the beads prepared andthe thermal activation conditions employed are given in Table III below.

                  TABLE III                                                       ______________________________________                                                        T in ° C.                                                              600° C.                                                                       900° C.                                                                        1,000° C.                               THERMAL           Time in hours                                               ACTIVATION        2 hours  1 hour  1 hour                                     ______________________________________                                        Characteristics of the beads obtained                                         TD (g/cm.sup.3)   0.46     0.44    0.44                                       TPV (cm.sup.3 /g) 100.00   1.05    1.05                                       DIS                                                                           <100 Å        0.03     0.01    0.00                                       100-1,000 Å   0.64     0.68    0.69                                       1,000-5,000 Å 0.08     0.10    0.09                                       5,000-10,000 Å                                                                              0.08     0.07    0.06                                       >10,000 Å     0.17     0.19    0.21                                       SSA (m.sup.2 /g)  185      107     92                                         PPC (kg)          3.8      3.6     3.6                                        AR (%)            99.7     99.7    99.7                                       HT 982° C.                                                             SSA (m.sup.2 /g)  75       75      75                                         PPC (kg)          3.3      3.3     3.3                                        AR (%)            99.6     99.6    99.6                                       Sh (%)            0.8      0.8     0.8                                        HT 1,093° C.                                                           SSA (m.sup.2 /g)  71       71      71                                         PPC (kg)          3.8      3.8     3.8                                        AR (%)            99.7     99.7    99.7                                       HT H.sub.2 O, 900° C.                                                  SSA (m.sup.2 /g)  84       84      84                                         PPC (kg)          3.4      3.4     3.4                                        AR (%)            99.4     99.4    99.4                                       ______________________________________                                    

EXAMPLE 7

This comparative example illustrates the treatment process described inU.S. Pat. Nos. 3,628,914 and 3,480,389.

The procedure of Example 1 was followed, except that the treatmentmedium was either nitric acid by itself, acetic acid by itself, orformic acid by itself.

The physical characteristics and properties of the beads prepared aretabulated below in Table IV.

                  TABLE IV                                                        ______________________________________                                                      TREATMENT MEDIUM                                                                Nitric acid                                                                            Acetic acid                                                                             Formic acid                                                by itself                                                                              by itself by itself                                                  7 g per  10 g per  6 g per                                                    100 g of 100 g of  100 g of                                   CONCENTRATION   Al.sub.2 O.sub.3                                                                       Al.sub.2 O.sub.3                                                                        Al.sub.2 O.sub.3                           ______________________________________                                        Characteristics of the beads obtained                                         TD (g/cm.sup.3) 0.49     0.50      0.50                                       TPV (cm.sup.3 /g)                                                                             0.91     0.89      0.89                                       DIS                                                                           <100 Å      0.03     0.04      0.04                                       100-1,000 Å 0.48     0.49      0.48                                       1,000-5,000 Å                                                                             0.16     0.07      0.08                                       5,000-10,000 Å                                                                            0.13     0.08      0.08                                       >10,000 Å   0.10     0.21      0.21                                       SSA (m.sup.2 /g)                                                                              103      95        92                                         PPC (kg)        3.2      3.1       3.0                                        AR (%)          98.1     98.0      97.5                                       HT 982° C.                                                             SSA (m.sup.2 /g)                                                                              54       47        45                                         PPC (kg)        2.8      2.6       2.5                                        AR (%)          97.7     97.5      97.2                                       Sh (%)          1.5      2.1       2.3                                        HT 1,093° C.                                                           SSA (m.sup.2 /g)                                                                              47       44        43                                         PPC (kg)        2.5      2.2       2.1                                        AR (%)          97.2     97.1      96.9                                       HT H.sub.2 O, 900° C.                                                  SSA (m.sup.2 /g)                                                                              49       49        48                                         PPC (kg)        2.9      2.9       2.7                                        AR (%)          97.9     97.8      97.1                                       ______________________________________                                    

Upon a comparison of the characteristics and properties of the aluminabeads obtained in accordance with this comparison example, it is foundthat the beads obtained in accordance with the processes of the priorart do not possess the exceptional mechanical, thermal and hydrothermalproperties of the alumina of the present invention. Furthermore, theprior art processes do not permit one to increase the total pore volumeand the pore volume of pores having a diameter of between 100 and 1,000Å to advantageous proportions.

Moreover, while the processes of the prior art lead to beads possessinga TPV which is less than the TPV obtained by the process of the presentinvention, they also lead to beads possessing a much lower mechanicalstrength (PPC).

While the invention has been described in terms of various preferredembodiments, the skilled artisan will appreciate that variousmodifications, substitutions, omissions, and changes may be made withoutdeparting from the spirit thereof. Accordingly, it is intended that thescope of the present invention be limited solely by the scope of thefollowing claims.

What is claimed is:
 1. In a process for the treatment of exhaust gasesof an internal combustion engine, for the hydrogen treatment ofpetroleum products, for the recovery of sulfur from sulfur compounds,for dehydration, reforming, steam reforming, dehydrohalogenation,hydrocracking, hydrogenation, dehydrogenation or dehydrocyclization ofhydrocarbons or other organic compounds, and for oxidation and reductionreactions, wherein alumina agglomerates are employed as a catalystsupport in said process, the improvement which comprises, obtaining saidalumina agglomerates by(i) preparing a ground or unground powder ofactive alumina having a poorly crystalline structure, an amorphousstructure or an admixture of said structures; (ii) agglomerating saidactive alumina powder to form alumina agglomerates; (iii) combining (a)at least one acid selected from the group consisting of nitric acid,hydrochloric acid, perchloric acid, and sulfuric acid, and (b) at leastone compound providing an anion capable of combining with aluminum ionsin solution selected from the group consisting of nitrate, chloride,sulfate, perchlorate, bromoacetate and dibromoacetate salts and salts ofmonocarboxylic acids to form an aqueous treatment medium, wherein theconcentration of the acid in the aqueous medium is less than 20% byweight and the concentration of the anion donor compound is less than50% by weight and wherein the quantity of the acid is in an amounteffective to dissolve from 0.5% to about 15% by weight of the aluminaagglomerates, and subjecting said agglomerates to an aqueous mediumtreatment by contacting said agglomerates with said aqueous treatmentmedium; (iv) subjecting the combined agglomerates and the aqueoustreatment medium to a hydrothermal treatment by heating at a temperaturein the range of from about 80° C. to about 250° C., wherein thecombination of said aqueous medium treatment and hydrothermal treatmentincreases the porosity of the agglomerates by expansion; and then (v)thermally activating the agglomerates at a temperature in the range offrom about 500° C. to about 1100° C., with essentially no loss ofalumina agglomerates treated as a result of the combination of steps(iii)-(v).
 2. The process of claim 1, wherein the hydrothermal treatment(iv) is conducted simultaneously with the aqueous medium treatment(iii).
 3. The process of claim 1, wherein the agglomerates are driedprior to the thermal activation.
 4. The process of claim 1, wherein thehydrothermal treatment is conducted for a period of time ranging from afew minutes to about 36 hours.
 5. The process of claim 1, wherein theacid concentration is between 1% and 15% by weight.
 6. The process ofclaim 1, wherein the compound concentration ranges from about 3% toabout 30% by weight.
 7. The process of claim 1, wherein the compoundproviding an anion capable of combining with aluminum ions in solutionprovides anions A^(-n) which form products with aluminum ions insolution in which the atomic ratio ##EQU7##
 8. The process of claim 1,wherein the hydrothermal treatment is conducted at a temperature in therange of from about 120 to about 220° C. for a period of time rangingfrom about 15 minutes to about 18 hours.
 9. The process of claim 1,wherein the alumina agglomerates are comprised of a plurality ofacicular platelets, said agglomerates being of an average size of fromabout 1 to 20 microns with at least about 50 percent of said plateletshaving a dimension along their axis of greatest development of betweenabout 0.05 to 5 microns, the ratio of said dimension to the averagewidth of said platelets ranging from about 2:1 to 20:1, and the ratio ofsaid dimension to the average thickness of said platelets ranging fromabout 1:1 to 500:1.
 10. The process of claim 9, wherein at least about50 percent of said platelets have a dimension along their axis ofgreatest development of between about 0.1 to 2 microns.
 11. The processof claim 9, wherein the ratio of said dimension along the axis ofgreatest development to the average width ranges from about 5:1 to 15:1and wherein the ratio of said dimension to the average thickness rangesfrom about 10:1 to 200:1.
 12. The process of claim 9, wherein saidagglomerates are substantially spherical in shape.
 13. The process ofclaim 9, wherein said agglomerates are between about 2 to 10 microns indimension.
 14. The process of claim 1, wherein the alumina agglomeratespossess a total pore volume of between about 0.36 to about 0.75 g/cm³.15. The process of claim 1, wherein the alumina agglomerates possess apore size distribution such that

    ______________________________________                                        φ Å                                                                         <100    100-1,000                                                                              1,000-5,000                                                                           5,000-10,000                                                                           >10,000                               ______________________________________                                        ν cm.sup.3 /g                                                                    0-0.10  0.40-0.90                                                                              0-0.60  0-0.55   0-0.40                                ______________________________________                                         in which Φ represents the diameter of the pores and ν the volume of     pores having a diameter between the limits indicated.


16. The process of claim 1, wherein the alumina agglomerates possess:atapped density of between about 0.36 and about 0.75 g/cm³, a total porevolume of between about 0.35 and about 1.50 cm³ /g, a pore sizedistribution such that

    ______________________________________                                        φ Å                                                                         <100    100-1,000                                                                              1,000-5,000                                                                           5,000-10,000                                                                           >10,000                               ______________________________________                                        ν cm.sup.3 /g                                                                    0-0.10  0.40-0.90                                                                              0-0.60  0-0.55   0-0.40                                ______________________________________                                    

in which Φ represents the diameter of the pores and ν the volume ofpores having a diameter between the limits indicated, a specific surfacearea of between 80 and about 200 m² /g, a mechanical strength of betweenabout 2 and 20 kg, an attrition resistance greater than 98%, a shrinkageof less than 2%,and which aluminum agglomerates after a heat treatmentat 982° C. for 24 hours under dry air possess physical characteristicsof a specific surface area greater than 60 m² /g, mechanical strength ofbetween 2 and 20 kg, attrition resistance greater than 98%, shrinkageless than 2%,and which alumina agglomerates after a heat treatment at1093° C. for 24 hours under dry air possess physical characteristics ofa specific surface area greater than 50 m² /g, mechanical strength ofbetween 2 and 20 kg, attrition resistance greater than 98%,and whichalumina agglomerates after a hydrothermal treatment at 900° C. for 24hours under a nitrogen atmosphere containing 10% steam possess physicalcharacteristics of specific surface area greater than 60 m² /g,mechanical strength of between 2 and 20 kg, and attrition resistancegreater than 98%.